The longer you're in the air (all else equal), the tougher the landing will be on you*, particularly if you (correctly) do a "slide-out" landing with the legs well extended.
A 2 1/2 hitch takes a while to perform, so is used mostly by people who are indeed in the air a long time, e.g.
http://www.youtube.com/watch?v=Gfp2JZpEGfg
(sorry for mediocre video quality--the slomo parts are a bit better).
So it's accurate to say the 2 1/2 is tough on you (and you're right, a technique that takes a while to learn to land properly), but I think it's more because most people who can even *use* the 2 1/2 are hitting the sand at a much higher speed than most folks do.
My problem in teaching a 2 1/2 (even a 1 1/2, with some) is that it *does* take a while to perform, and it's easy to "anticipate" the midair movements while still taking off, just to get all the arm circling done. This ruins the takeoff position/drive.
One example from my early coaching days: I coached a novice (female) jumper who covered about 5m, sailing, on her first day of trying the event. Okay, I thought, let's get her hitching and she'll be outstanding!
Instead, by the middle of the year I had coached her down maybe 30cm from that first day. Reason: She was so anxious to get the hitching in that she started doing it before her takeoff was complete. I finally saw reason, switched her to a hang, and she gained about 50cm in a short time and won the Ivy League championship.
By the way, because the hang slows the jumper's forward rotation, it not only puts him/her in a better *landing* position than the sail does**, it also makes the legs typically land with less of a thud. Compare that to the (now outlawed) somersault technique, which exaggerated the forward rotation. When that technique was done properly, great takeoffs and huge extension on landing were possible--but the legs often tended to "slam" down on the landing, with a thud you could sometimes hear across the field. Ow.
*This is one answer to those who want to know why Bolt won't try LJ. He would hit the sand with a *lot* of force, and has no need to risk it.
For me, all this makes Carl's four OG golds in the LJ that much more impressive. Just holding together physically for that long is *tough*.
**Of course, the hitch slows down the rotation even more, and makes those scoop/slide-out landings easier to execute.